In telecommunications, high speed core networks mainly rely on optical transmission. Data signals can be modulated onto optical carriers at different wavelengths and transmitted together using wavelength division multiplexing over a same fiber span. In long-haul optical transmission, optical regenerators are provided along an optical transmission line to regenerate optical signals and remove distortions. Moreover, Forward Error Correction (FEC) processing can be applied to increase the maximum transmission distance per span and the receiver sensitivity.
With the introduction of wavelength selective switches (WSS) and reconfigurable optical add/drop multiplexers (ROADMs), optical transmission networks evolve from classical point-to-point transmission more and more towards optical switched network applications, so that transmission distances may be different for signals at different wavelength channels.